In such apparatus for generating electric power, it is known to use a gas holder between the gasifier and the gas engine or other equipment utilized in the fuel gas produced in order to be able to control the production and use separately and compensate for fluctuations in fuel gas production and thus maintain a constant electrical output power.
From FR 2,844,804 it is known to use the gas provided in a downdraft gasifier as fuel for a gas engine producing electrical power. The produced gas is furthermore used as fuel for a burner for heating purposes. Varying gas production is stated to be partially taken up by the mechanical inertia of the gas engine. Obviously, such varying gas production can also be taken up by varying the supply of gas to the burner. One major disadvantage of the downdraft gasifier is that the produced gas is delivered at a high temperature of approximately 500-650° C., which has to be cooled down immediately in order to reduce explosion risk. After cooling down, several further steps of cleaning, scrubbing and filtering are performed before the gas can be used in the gas engine. This document furthermore specifies that the biomass fuel delivered to the gasifier is dewatered, dried and pelletized biomass having a well-defined moisture content of 10-25%. Nothing is indicated in this document relating to the specification of the gasifying agent except that atmospheric air is used for drying, pyrolysis, reduction and oxidation.
From US 2004/0168468 A1 and GB 2 331 128 A it is known to deliver gas from a high-pressure gasifier to a gas turbine producing electricity. The high-pressure gasifiers are suited for gasifying particulate fossil fuels such as coal or residues from petroleum industry, and produce fuel gas at a high temperature in the range of 500-1000° C. A main disadvantage with such high-pressure gasifiers is that the gasifier confinement has to be a pressure vessel, and that supply of fuel and gasifying agent to the gasifier has to be performed at the high pressure of the gasifier, thus involving use of high-pressure compressors for delivery thereof.
US 2004/0168468 A1 describes an automatic up- and down-variation of the solid-fuel feed flow to the gasifier based on the monitored output electric generator output. Furthermore, this document describes a sophisticated and complicated air separation system, where the air is separated in two streams consisting of N2 and O2, respectively, in order to provide pure oxygen as gasifying agent in the high-pressure, high-temperature gasifier, and in the combustion device, i.e. the gas turbine, the separated N2 is introduced in order to cool down the gas turbine
GB 2, 331, 128 A uses a high-pressure buffer flue gas storage, or as an alternative the high-pressure gasifier system itself is used as a buffer gas storage.